There are known surface acoustic wave (SAW) devices that have an IDT (Interdigital Transducer) having a pair of comb electrodes on a piezoelectric substrate, as acoustic wave devices using an acoustic wave. The SAW devices are used for band pass filters of wireless communication devices that process a wireless signal in a frequency band of 45 MHz to 2 GHz, as presented by mobile phones. Recently, as performance of wireless communication devices are enhanced (for example, multi-band or multi-mode), low loss of filters are demanded in order to improve receiving sensitivity or reduce power consumption. Factors of the loss of the SAW devices are such as a leakage of an acoustic wave in an opening length direction, a leakage of an acoustic wave in a propagating direction, a loss of conversion from an acoustic wave to a bulk wave, a resistance loss of a comb electrode.
Various SAW devices are supposed in order to reduce a loss of a filter. For example, there are supposed SAW devices that have a structure in which an insulating material is buried between an edge of an electrode finger and an edge of a dummy electrode finger (see Japanese Patent Application Publication No. 2009-278429). There are supposed SAW devices that have a structure in which a part of a bus bar is thicker than an electrode finger (see Japanese Patent Application Publication No. 2004-328196).
However, conventional SAW devices cannot reduce a loss sufficiently. There is a room for improvement.